The present invention relates to a working fluid comprising a refrigerant and a refrigeration lubricant which is used in refrigerating cycle equipment of refrigerant compression-type.
In the refrigerating cycle equipment of refrigerant compression-type such as air conditioners, electric refrigerators (freezers), refrigerating or freezing warehouses and refrigerating show cases, hydrocarbons containing a fluorine atom have conventionally been employed as refrigerant.
In particular, hydrocarbons containing a chlorine atom in addition to the fluorine atom have long been employed as the refrigerant having excellent performance such as non-flammability or the like. These chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) contain a chlorine atom. It has now been clarified that these refrigerants destruct the ozone layer when they are released to the open air and reached the stratosphere, and the use of them has recently been limited or inhibited globally.
At present, hydrofluorocarbons (HFC) containing no chlorine atom have begun to be employed in stead of these refrigerants. Although the HFC has no potential for destroying the ozone layer, it demonstrates a high greenhouse effect because its life in the air is long. Thus, the HFC is not necessarily an excellent refrigerant in the viewpoint of preventing the global warming which is a problematic concern in recent years.
Instead of the above-mentioned hydrocarbons containing a halogen atom, hydrocarbons containing no halogen atom, which are inflammable but have an ozone layer depletion potential (ODP) of zero and a very small global warming potential (GWP) as compared to the hydrocarbons containing a halogen atom, are now employed as the refrigerant. The refrigerating cycle equipment employing this refrigerant is practically used as the refrigerator and feasibility of the refrigerant for developing large-size equipment is now under investigation. In particular, iso-butane is used for the electric refrigerators and propane is used for the air conditioners as the hydrocarbon refrigerant in practical, respectively.
Further, together with the change of the refrigerant, various modifications or designs have been investigated with respect to the materials in the refrigerating cycle equipment.
For example, with respect to the refrigeration lubricant as a component of the working fluid which is employed together with the refrigerant, mineral oils and alkylbenzene compounds which were conventionally employed as the refrigeration lubricant could not be used with the recent trend for shifting the refrigerant to the ozone layer nondestructive HFC such as R-134a (1,1,1,2-tetrafluoroethane), because they have no compatibility with such refrigerant. In a refrigerating cycle of refrigerant compression-type, a portion of the refrigeration lubricant is discharged from the compressor together with the refrigerant. Therefore, the refrigeration lubricant must not be separated from the refrigerant and stayed in the refrigerating cycle (other than the compressor) in order to secure an amount of oil required for lubricating the mechanism of circulating the refrigerant through the refrigerating cycle with a low temperature part and returning the same to the compressor.
For these reasons, it has been believed that the refrigeration lubricant should have compatibility with the refrigerant. In the refrigerating cycle equipment, which employs the HFC as the refrigerant, glycol ether oils or polyol ester, oils are mainly used as the refrigeration lubricant. In a limited number of equipment, alkylbenzene oils, which are incompatible with the HFC refrigerant are used (JP-A-5-157379).
In addition, various carbonate oils are proposed as the refrigeration lubricant for the HFC refrigerant (JP-A-3-149295, JP-A-3-247695, and others).
On the other hand, hydrocarbons containing no halogen atom such as ethane, propane, butane, iso-butane and the like are used as the refrigerant. As well as the less polar mineral oils and alkylbenezene oils which have been used with the (hydro) fluorocarbons containing a chlorine atom the much polar glycol ether oils and polyol ester oils, which have been used with the hydrofluorocarbons containing no chlorine atom, have a high compatibility with the hydrocarbon refrigerant containing no halogen atom. Therefore, it has been believed that there is no problem in selecting the refrigeration lubricant.
In the case of employing the above-mentioned refrigeration lubricants such as mineral oils, alkylbenzene oils, glycol ether oils and polyol ester oils, however, their compatibilities with the refrigerant is excessive and the amount of the refrigerant to be dissolved in the refrigeration lubricant becomes excessively large. Namely, there is a problem that a refrigerating cycle equipment could not sufficiently demonstrate its performance if a large amount of the refrigerant is charged in the equipment. On the other hand, since hydrocarbons such as ethane, propane, butane, iso-butane and the like are inflammable, it is preferable that the amount of the hydrocarbons is possibly decreased in a range wherein the refrigerating cycle equipment operates efficiently and performs its ability.
In addition, in refrigerating cycle equipment employing a HFC refrigerant together with an alkylbenzene oil which has no compatibility with the HFC, the specific gravity of the HFC refrigerant is larger than that of the refrigeration lubricant. Therefore, there is a further problem that an oiling mechanism for a sliding part of a refrigerant compressor, an oil returning mechanism for the refrigeration lubricant component circulating through the refrigerating cycle, or a driving control mechanism becomes complicated.
It is therefore the object of the present invention to provide a working fluid which demonstrates preferable performance even with the small amount of the refrigerant containing no halogen atom such as ethane, propane, butane, iso-butane or the like in the refrigerating cycle equipment.